What does it mean if I can hear the person on the other line but they can not hear me?

What does it mean f I can hear the person on the other line but they can not hear me?

This is a hardware issue. Your bottom mic is not functioning properly. The mic operation is made up of three components, put together the mic operates properly. The components include: Charging dock flex cable, Housing speaker and the Circuit board. Unfortunately only 2 of the first 3 components are interchangeable. If the mic issue is resolved from changing out the Charging dock flex cable and/or Housing speaker then you will have verified that the circuit board is fine. If you are still having mic issues after changing out both the Charging dock flex cable and Housing speaker you will have now verified that the circuit board is bad. Which means you have a fancy iPod Touch going forward. The circuit board(motherboard) is the only part that can not be repaired, the circuit board is the 1 component in any idevice or any piece of electronic that once the circuit board becomes bad you might as well at this point plan on purchasing a new unit. Unless you have a spare iPhone laying around that you can pull the circuit board from. If you ever look up the cost for circuit boards that sellers pull from used iPhones you will fully understand why at this point it is more cost efficient to purchase a new unit with a new manufacturer warranty.